diff --git a/src/libosmo-mgcp/mgcp_sdp.c b/src/libosmo-mgcp/mgcp_sdp.c
index a7478ad..5fa6bdb 100644
--- a/src/libosmo-mgcp/mgcp_sdp.c
+++ b/src/libosmo-mgcp/mgcp_sdp.c
@@ -478,6 +478,8 @@
 
 	for (i = 0; i < fmtp_params_len; i++) {
 		rc = msgb_printf(sdp, "a=fmtp:%u", fmtp_params[i].payload_type);
+		if (rc < 0)
+			return -EINVAL;
 
 		/* Add amr octet align parameter */
 		if (fmtp_params[i].param.amr_octet_aligned_present) {